1. Field of the Invention
The present invention relates in general to a rotary cutting saw which includes a base disk and a plurality of abrasive segments bonded to the outer circumferential surface of the base disk and which is used for cutting, parting or grinding an asphalt, a concrete, a building material or other work material. More particularly, the invention is concerned with such a cutting saw having slits formed in the outer circumferential surface of the base disk and located between the abrasive segments.
2. Discussion of the Related Art
There is known a rotary cutting saw 110, as shown in FIG. 6, consisting principally of a base disk 111 which is made of a tool steel or other metallic material, and a plurality of abrasive segments 112 which are bonded to the outer circumferential surface of the base disk 111 so as to be circumferentially spaced apart from each other at a constant angular interval therebetween. In portions of the outer circumferential surface of the base disk 111 each of which is located between adjacent ones of the abrasive segments 112, there are formed cutouts or slits 113 each of which extends inwardly in the radial direction of the base disk 111 from the outer circumferential surface of the base disk 111, and also in the axial direction of the base disk 111 over the entire axial length of the base disk 111. Each abrasive segment 112, which is referred to also as a segment chip, consists of a small piece including diamond abrasive grains or other super abrasive grains which are held together with a metal bond or other bonding agent. This rotary cutting saw 110 is a tool which is generally referred also to as a cutting blade, a rotary blade, a cutting grindstone or a grinding wheel, and which is generally used for cutting, parting or grinding an asphalt, a concrete, a building material or other work material, for example.
Each slit 113 is defined by a pair of opposed side surfaces 113a, 113b and a part-cylindrical surface 113c. The side surfaces 113a, 113b are opposed to each other and parallel to the radial direction of the base disk 111. The part-cylindrical surface 113c defines a part of a cylinder having an axis which is parallel to the axial direction of the base disk 111 and which lies on a center plane between the side surfaces 113a, 113b. The part-cylindrical surface 113c connects radially inner end portions of the respective side surfaces 113a, 113b. The slits 113 facilitate dissipation or radiation of a heat generated when the abrasive segments 112 are bonded to the base disk 111, thereby preventing the base disk 111 from being affected by the heat. The slits 113 permit, during a cutting or parting operation with the rotary cutting saw 110, a cutting fluid to be easily applied to a cutting point at which the work material is cut by the abrasive segments, and also permit cutting chips that are produced at the cutting point to be removed from a groove being currently formed in the work material, thereby improving the cutting or parting performance of the rotary cutting saw 110.
The rotary cutting saw 110 suffers from a drawback, particularly, when used in successive or repeated operations for cutting or parting the work materials. That is, the cutting chips produced in the cutting operations tend to be concentrated in a xe2x80x9cneckxe2x80x9d portion of the rotary cutting saw 110, i.e., a radially outer end portion of the base disk 111 which is radially adjacent to the abrasive segments 112, whereby the neck portion is worn and thinned due to rubbing thereof against the cutting chips, possibly causing breakage of the abrasive segments 112.
In view of the above drawback, there has been proposed a rotary cutting saw, as disclosed in JP-Y-56-36967 and JP-Y-01-31422, which includes wear-resistant chips made of a cemented carbide or ceramic material having a high degree of wear resistance. Each wear-resistant chip is bonded to one of the opposed side surfaces of the corresponding slit, in the interest of reducing wear of the neck portion of the rotary cutting saw.
There has been also proposed a rotary cutting saw, as disclosed in JP-A-59-110563 and JP-U-05-5355, which includes wear-resistant chips having respective lengths different from each other, and slits having respective depths or radial lengths different from each other. Each wear-resistant chip, which is made of cemented carbide or ceramic material, is bonded to one of the opposed side surfaces of the corresponding slit whose radial length corresponds to the length of the wear-resistant chip. This construction prevents flows of the cutting chips along a single circle having a given radius, namely, prevents the cutting chips from being concentrated at a single radial portion of the base disk, and facilitates the cutting chips to be dispersed so as to be distributed into a plurality of radial portions of the base disk, e.g., a plurality of mutually concentric circles having different radii, so that amount of wear of the neck portion of the rotary cutting saw is reduced.
However, in each of the above-described conventional rotary cutting saw in which the wear-resistant chip is bonded to one of the opposed side surfaces of each slit, a plurality of small turbulent or eddy flows of the cutting chips are generated in each slit during a cutting operation, due to the presence of a stepped or protruding portion in the inner surface of the slit, thereby impeding entrance of the cutting chips into the slits and accordingly causing the cutting chips to stay in the groove being currently formed in the work material. A portion of the base disk which portion is adjacent to the wear-resistant chip, i.e., the neck portion of the rotary cutting saw is still likely to be somewhat worn by the cutting chips staying in the currently formed groove of the work material. That is, the wear in the neck portion is not satisfactorily prevented even in the above-described known cutting saw. Further, the wear-resistant chip bonded to one of the side surfaces of the slit inevitably reduces a spacing between the side surfaces. The reduced spacing between the side surfaces of the slit causes a reduced efficiency of discharge of the cutting chips from the currently formed groove and a reduced efficiency of application of the cutting fluid to the cutting point, thereby resulting in a reduced cutting efficiency or a reduced durability of the cutting saw.
It is therefore an object of the present invention to provide a rotary cutting saw constructed to reduce an amount of wear of its neck portion without deteriorating its cutting performance.
Various studies conducted by the present inventors under the above-described situation revealed that the wear of the neck portion of the cutting saw is reduced by suitably designing the shape of each slit formed in the outer circumferential surface of the base disk of the cutting saw. For example, the inventors found a fact that the wear of the neck portion is advantageously reduced where the opposed side surfaces of the slit are connected at their respective radially inner end portions to the part-cylindrical surface which has an inside diameter larger than a circumferential distance between the radially inner end portions of the opposed side surfaces, such that one of the side surfaces is smoothly connected to the part-cylindrical surface without a stepped or protruding portion therebetween.
It is assumed that, in a cutting operation with the conventional cutting saw, a plurality of small eddy flows of the produced cutting chips with a cutting (cooling) fluid are generated within each slit, and the time for which the cutting chips stay in the slit is generally reduced due to turbulent flows occurring as a result of mutual collisions of the small eddy flows. That is, the turbulent flows tend to undesirably cause movements of the cutting chips out of each slit, so that most of the cutting chips are likely to be discharged from each slit, before a certain amount of angular displacement of the cutting saw relative to the work material is completed after the production of the cutting chips, namely, before the slit comes out of the currently formed groove with the rotation of the cutting saw after the production of the cutting chips. In other words, the turbulent flows tend to impede movements of the cutting chips into each slit, so that most of the cutting chips are unlikely to be caught in each slit before the slit comes out of the currently formed groove after the production of the cutting chips.
The above-described fact found by the present inventors is explainable by assuming that a small number of comparatively large eddy flows (e.g., a single flow) of the cutting chips are formed, in place of the turbulent flows, within each slit where the part-cylindrical surface is smoothly connected to one of the side surfaces without a stepped or protruding portion, and that the time for which the cutting chips stay in the slit is generally increased owing to the large eddy flow. That is, the large eddy flow tend to advantageously impede movements of the cutting chips out of each slit, or facilitate movements of the cutting chips into each slit, so that the ratio of ones of the produced cutting chips, which are caught in each slit and then carried by each slit out of the currently formed groove, to the entirety of the produced cutting chips is increased. Thus, an increased amount of the cutting chips are discharged from the groove after the slit comes out of the groove, thereby minimizing an amount of the cutting chips forced to be displaced into a small gap between the base disk and each side surface of the currently formed groove, and accordingly resulting in a reduced amount of wear of the base disk.
The above object may be achieved according to the principle of the present invention, which provides a rotary cutting saw comprising: a base disk; and a plurality of abrasive segments which are bonded to an outer circumferential surface of the base disk so as to be spaced apart from each other in a circumferential direction of the base disk; wherein the base disk has a plurality of slits which are formed in the outer circumferential surface of the base disk so as to be located between adjacent ones of the abrasive segments in the circumferential direction, each of the plurality of slits extending inwardly in a radial direction of the base disk from the outer circumferential surface of the base disk, and extending in an axial direction of the base disk over an entire axial length of the base disk; wherein each of the slits is defined by a pair of side surfaces opposed to each other in the circumferential direction, and a part-cylindrical surface defining a part of a cylinder having an axis which is parallel to the axial direction, the side surfaces being connected at radially inner end portions thereof to the part-cylindrical surface; wherein the part-cylindrical surface has a width as measured in the circumferential direction, which width is larger than a circumferential distance between the radially inner end portions of the side surfaces; and wherein the part-cylindrical surface is smoothly connected to one of the side surfaces without a stepped portion therebetween.
In the rotary cutting saw of the present invention, the opposed side surfaces of each slit are connected at their respective radially inner end portions to the part-cylindrical surface that has the circumferential width larger than the circumferential distance between the radially inner end portions of the side surfaces, and the part-cylindrical surface is smoothly connected to one of the side surfaces without a stepped portion therebetween. According to this arrangement, there is formed a single or small number of large eddy flow within each slit during a cutting operation. The large eddy flow advantageously impedes movements of the cutting chips out of each slit, or facilitates movements of the cutting chips into each slit, so that an increased amount of the cutting chips are caught in each slit and then carried by each slit out of the currently formed groove so as to be discharged from the groove after the slit comes out of the groove, thereby resulting in a reduced amount of wear in the neck portion of the base disk. This advantage can be obtained, for example, even without bonding a wear-resistant chip to one of the side surfaces of the slit. Therefore, the rotary cutting saw of the present invention does not suffer from a reduced efficiency of discharge of the cutting chips from the currently formed groove or a reduced efficiency of application of the cutting fluid to the cutting point, which would be caused by the presence of the wear-resistant chip, and which would reduce the cutting performance and the durability of the cutting saw. It is noted that the cylinder partially defined by the part-cylindrical surface of each of the slits may have a circular shape or an elliptical shape in a cross section perpendicular to the axial direction of the base disk.
According to a first preferred form of the invention, the above-described one of the side surfaces of each of the slits corresponds to a tangent plane which is tangent, at the intersection of the above-described one of the side surfaces and the part-cylindrical surface, with respect to the part-cylindrical surface.
According to a second preferred form of the invention, the side surfaces of each of the slits are parallel to the radial direction, and wherein the axis of the above-described cylinder is offset, in the circumferential direction by a predetermined amount, from a center plane between the side surfaces. The axis of the cylinder of each of the slits may lie on an extension of the other of the side surfaces which is other than the above-described one of the side surfaces, so that the circumferential width of the part-cylindrical surface is made about twice as large as the circumferential distance between the side surfaces, thereby further facilitating generation of a large eddy flow of the cutting chips within each slit.
According to a third preferred form of the invention, the above-described one of the side surfaces of each of the slits is located on the forward side of the other of the side surfaces as viewed in a rotating direction of the base disk. This arrangement permits easy formation of the large eddy flow of the cutting chips, since the cutting chips tend to be displaced, from a cutting point in which the work material is cut by the abrasive segment, inwardly in the radial direction of the base disk and forwardly in the rotating direction of the base disk.
According to a fourth preferred form of the invention, the axis of the cylinder of each of the slits lies on a center plane between the side surfaces, and wherein the above-described one of the side surfaces includes a radially-outer-part surface and a radially-inner-part surface which are contiguous to each other, the radially-outer-part surface being parallel to the other of the side surfaces, the radially-inner-part surface being inclined with respect to the radially-outer-part surface such that the radially-inner-part surface corresponds to a tangent plane which is tangent, at the intersection of the radially-inner-part surface and the part-cylindrical surface, so that the part-cylindrical surface is smoothly connected to the above-described one of the side surfaces.
It is appreciated that each slit 113 of the above-described conventional cutting saw 110 of FIG. 6 has a shape which is identical to a shape defined by the above-described radially-outer-part surface, an extension of the radially-outer-part surface that extends inwardly in the radial direction, the other side surface, and the part-cylindrical surface which intersects with the other side surface and the extension of the radially-outer-part surface. Therefore, the rotary cutting saw of this fourth preferred form of the invention can be produced by slightly modifying the conventional cutting saw, namely, by simply removing a stepped portion, which is located at the intersection of the part-cylindrical surface and the extension of the radially-outer-part surface, down to the above-described radially-inner-part surface.
According to one advantageous arrangement of the fourth preferred form of the invention, the above-described one of the side surfaces of each of the slits is located on the forward side of the other of the side surfaces as viewed in a rotating direction of the base disk.
According to a fifth preferred form of the invention, the slits have respective depths as measured in the radial direction, which depths are different from each other. In the rotary cutting saw of the fifth preferred form of the invention, the cutting chips are prevented from being concentrated at a single radial portion of the base disk, and are easily dispersed so as to be distributed into a plurality of radial portions of the base disk, e.g., a plurality of mutually concentric circles having different radii, thereby leading to an increased efficiency of discharge of the cutting chips from the currently formed groove and an increased efficiency of application of the cutting fluid to the cutting point, so that amount of the wear of the neck portion of the rotary cutting saw is reduced. It is noted that the side surfaces of the slits may have the respective radial lengths different from each other, and that the part-cylindrical surfaces of the slits may have the respective circumferential widths different from each other.
According to a sixth preferred form of the invention, the plurality of slits include at least one first slit and at least one second slit which are alternately arranged in the circumferential direction, the first slit having a depth as measured in the radial direction, which depth is larger than that of the second slit.
In the rotary cutting saw of this sixth preferred form of the invention, the cutting chips are prevented from being concentrated at a single radial portion of the base disk, and are easily dispersed so as to be distributed into a plurality of radial portions of the base disk, e.g., a plurality of mutually concentric circles having different radii, thereby leading to an increased efficiency of discharge of the cutting chips from the currently formed groove and an increased efficiency of application of the cutting fluid to the cutting point, so that amount of the wear of the neck portion of the rotary cutting saw is reduced. For example, the side surfaces of the first slit may have lengths larger than those of the side surfaces of the second slit. The inside diameter of the part-cylindrical surface of the first slit may be larger than the inside diameter of the part-cylindrical surface of the second slit.
In general, an increased amount of the cutting chips or cutting fluid can be accommodated in each slit, with increase of the circumferential distance between the side surfaces of the slit, or with increase of the inside diameter of the part-cylindrical surface, thereby facilitating discharge of the cutting chips from the currently formed groove of the work material as well as application of the cutting fluid to the cutting point. However, the strength of the base disk would be problematically reduced if all of slits have excessively increased sizes. Such a problem can be solved by the arrangement of this fifth preferred form of the invention in which the first slits each having the relatively large size and the second slits each having the relatively small size are alternately arranged in the circumferential direction, for assuring a required degree of strength of the base disk while facilitating the discharge of the cutting chips and the application of the cutting fluid so as to reduce amount of wear of the neck portion of the rotary cutting saw.
The part-cylindrical surface of each of the slits has an inside diameter of, preferably, 8-16 mm, and the ratio of the inside diameter of the part-cylindrical surface of the first slit to that of the part-cylindrical surface of the second slit is, preferably, 1.1-2.0. The depth of each of the slits is, preferably, 10-30 mm, and the ratio of the depth of the first slit to that of the second slit is, preferably, 1.1-3.0.
According to a sixth preferred form of the invention, the rotary cutting saw further includes a wear-resistant chip which has a width not smaller than the axial length of the base disk and which is bonded to one of the side surfaces of each of the slits, so that the wear-resistant chip protects this one of the side surfaces which is a part of the neck portion of the cutting saw, from being worn. The wear-resistant chip may be made of a cemented carbide or any other wear-resistant material. The wear-resistant chip may be attached to any one of the forward and backward side faces.